Immaculate Conceptionn. Roman Catholic Church The doctrine that the Virgin Mary was conceived free from all stain of original sin. The feast of the Immaculate Conception is celebrated on December 8.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Immaculate Conception n (Theology) Christian theol RC Church the doctrine that the Virgin Mary was conceived without any stain of original sin Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Immac?ulate Concep?tion n. 1. the doctrine according to which the Virgin Mary was conceived in her mother’s womb without the stain of original sin. 2. the feast commemorating this, celebrated on December 8. [1680?90] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.